247 831 pregnant women were studied (31 960 from the northern provinces having high rates of NTDs and 215 871 from the southern region of China with lower rates of NTDs); of the 31 960 women in the northern region, 18 591 women used folic acid, whereas 13 369 did not; in the southern region, 111 551 used folic acid, whereas 104 320 did not.

Among the women who did not take any folic acid, the rates of NTDs among offspring were 6.5 of 1000 pregnancies of at least 20 wk of gestation in the northern region and 0.8 of 1000 pregnancies of at least 20 wk of gestation in the southern region; among the fetuses or infants of the women who used any folic acid, the respective rates were 1.3 of 1000 (79% reduction; OR: 0.21; CI: 0.13–0.32) and 0.7 of 1000 (16% reduction; OR: 0.84; CI: 0.61–1.14) pregnancies of at least 20 wk gestation.